The present invention relates to a washing machine including an external cabinet, an outer tub installed inside the external cabinet, a spin basket rotatably installed inside the outer tub and a plurality of suspension units for suspending the outer tub with respect to the external cabinet, particularly, to a washing machine designed to effectively reduces.
A washing machine is generally provided with an external cabinet and vibratory system, which being constituted an outer tub and spin basket, suspended inside the external cabinet. The spin basket is rotatably installed in the outer tub for containing the laundry. The outer tub containing the spin basket is suspended inside the external cabinet by a plurality of suspension units.
During washing, rinsing and dehydrating operations of the washing machine, there are generated vibrations due to the rotation of the spin basket. The vibrations are severe especially when the load of the laundry is distributed in the spin basket in an unbalanced way. The vibrations of the spin basket are transmitted to the outer tub, to thereby generate vibrations and noises in the outer tub. Thus, the suspension units of the washing machine are provided with a damper for reducing the vibrations of the outer tub.
FIG. 10 shows a conventional washing machine. As shown in FIG. 10, a vibratory system 3 including an outer tub 4 and a spin basket 5 is elastically suspended inside an external cabinet 2 by a plurality of suspension units 61, each being installed at respective corners of the external cabinet 2. A pulsator (not shown) is installed inside the spin basket 5 to rotate washing water. A power transmission unit 9 having a driving motor (not shown) and a shaft assembly (not shown) is installed below the vibratory system. 3 to rotate the spin basket 5 or the pulsator selectively. The driving motor is operated according to a program stored in a controller (not shown) to make the washing machine perform washing, rinsing and dehydrating operations.
As shown in FIG. 10, the conventional suspension unit 61 includes a suspension bar 63 for connecting the outer tub 4 to the external cabinet 2 and a damper 65 installed at the lower end of the suspension bar 63 for supporting the outer tub 4. The damper 65 has a hollow cylinder (not shown) and a piston (not shown) frictionally slidable inside the cylinder, and the piston is combined with the lower end of the suspension bar 63. A balancer 6 is installed at the upper portion of the spin basket 5 to balance a rotation of the spin basket 5. In the above-described structure, when a vibration is generated to the vibratory system 3, that is, the outer tub 4 due to the rotation of the spin basket 5, the piston slides along up and down inside the cylinder, to thereby reduce the vibrations transmitted to the outer tub 4 by the frictional force between the cylinder and the piston.
The vibration of the vibratory system 3 and a cause thereof will be described in detail with reference to FIG. 11. The vibration of the vibratory system 3 may be divided into a translational movement and a rotational movement. The translational movement includes X-, Y- and Z-directional components, and the rotational movement includes pitching (P) with respect to the X-axis, yawing (Y) with respect to the Y-axis and rolling (R) with respect to the Z-axis, respectively. Here, since the Z-directional component of the translational movement and the rolling (R) with respect to the Z-axis, which are basic movement elements according to the operation of the vibratory system 3, are negligible with respect to the vibration of the vibratory system 3. On the other hand, the X- and Y-directional components of the translational movement and the pitching (P) and yawing (Y) with respect to the X- and Y-axes are unnecessary movement elements, which cause a noise and affect the endurance of the washing machine.
The vibration of the vibratory system 3 may be classified into a vibration generated at an initial stage of the dehydrating operation and a vibration generated at the time of an intermittent dehydration during the washing operation. Here, the vibration at the initial stage of the dehydrating operation is of translational movement, while the vibration at the time of the intermittent dehydration is of the rotational movement. Natural frequencies of the vibratory system with respect to the translational and rotational movements are 1.7 Hz (102 rpm) and 4.5 Hz (270 rpm), respectively.
The vibration at the initial stage of the dehydrating operation is caused by an unbalanced rotation of the spin basket 5. That is, when the load of the laundry is unbalanced inside the spin basket 5, the spin basket 5 rotates at an unbalanced state at a frequency range lower than a rotational frequency of 1.7 Hz. At this time, balancing balls (not shown) and a viscous fluid (not shown) in the balancer 6 may move toward the unbalanced load of the laundry. Accordingly, the spin basket 5 adds its unbalanced rotation so that the vibration of the spin basket 5 is increased to cause the noise.
On the other hand, at the time of the intermittent dehydration, the balancing balls and the viscous fluid start to move when the rotational frequency of the spin basket 5 exceeds 1.7 Hz, and the amplitude of the vibration depends on the location of the balancing balls and the viscous fluid at the frequency of 4.5 Hz. For example, if the balancing balls and the viscous fluid moving independently of the rotation of the spin basket 5 are located at the same side of the unbalanced laundry, the vibration becomes severe.
The vibration of the spin basket 5 which is transmitted to the outer tub 4 is decreased by the suspension unit 61.
However, the conventional suspension unit 61 is generally installed to the washing machine 60, based on a washing capacity of the washing machine 60 and experimental data under a no-load test. Thus, the vibration of the vibratory system 3, that is, of the outer tub 4 which is transmitted from the translational and rotational movements of the spin basket 5 can not be suitably decreased, thereby generating the noise to the washing machine. Also, the vibratory system 3 may collide with the external cabinet 2, to thereby obstruct a normal operation of the washing machine or to cause damage to the components of the washing machine.